GODIYMODULES 6-Digit LED Clock Kit: Assembly, Testing, Demonstration, 4 Hacks, Theory

Added: 2026-05-14

[00:00:00]Here's the Amazon listing. Um, DC 4.5 volt to 5.5 volt. So, it'll run on 5 volts. You could power it off a USB uh charger, that type of thing. although it doesn't have um a USB connector so you'd have to cut a connector off of a typical USB wall wart or you could use other batteries for sure. Uh 4 1/2 volts so you could power it off of three double A cells for example. Uh anyway, uh digital circuit clock kit, electronic clock teaching and practical training, welding and di uh do-it-yourself parts production by go DIY modules.

[00:00:57]$13. It's pretty much a steal considering all the parts that are on there. Um, I saw a YouTube video where somebody bought one of these and then issued the uh circuit board and just connected it all up uh with lots and lots of bus bar and made kind of a piece of sculpture out of it. Actually quite beautiful, but I don't want to go into that much effort.

[00:01:25]Now, they show it here as one board, but I'm pretty sure the board is supposed to kind of break in half somehow, so you don't have it laid out that way. Not sure. Um, they don't really seem to show it any other way.

[00:01:41]But the the main point about this one is that it's one of the few clock kits out there that do not use any monolithic um clock chips or a microprocessor or microcontroller of any kind. It's all discrete logic. And many people who got their start building digital logic for real, not, you know, in simulators and things, um, had the experience of designing their own clocks along the same lines as this, um, where you had to build an oscillator, you know, a reliable oscillator. you needed to divide it down to a appropriate clock signal, maybe a one second pulse or a pulse every 1 second rather, and then go through a series of uh decade counters and set them up with appropriate uh modulos. [snorts] So, for example, the uh counter that would handle the least significant digit would have a modulo of 10 and the one next to it would have a modulo of six because you only want it to count up to 59 seconds. And then you do the same thing there, a modulo 10 followed by a modulo 6.

[00:02:59]Um, and then [clears throat] you'd have another modulo 10. And then the uh most significant digit, depending how the clock would be set up, you'd only want it to go to a one or maybe uh a two if you're in 24hour mode. So you'd have to set up the modulo on that or just a reset. Um and you'd have to take all that into account when you're designing it and you'd learn a lot from it. But I just felt like building a kit and this looks like a cheap one and I can probably use it in my basement workshop or something. So, I thought I'd make a video about it.

[00:03:41]All right, the kit came in. It doesn't have any documentation, although uh the schematic is sort of kind of downloadable from Amazon's listing of the product.

[00:03:54]It's a really lowresolution photo of the schematic instead of the proper original of the schematic. So, a lot of the letters are really hard to make out.

[00:04:06]Even printed on 11 by7 like I've got it here. It's just a poor quality schematic, but enough to kind of figure out how it works. Pretty much useless for assembly. And you get the single circuit board. It's looks like fiberglass uh and um a black silk screen.

[00:04:32]Some weird stuff like this. I don't know what that's supposed to be. Looks like they had the same text twice, one on top of another.

[00:04:42]Or maybe that's somebody's logo.

[00:04:45]Anyway, there looks to be 1, two, 3, 4, 5, six.

[00:04:51]Um, I think those are display driver IC's.

[00:04:57]And then 1 2 3 4 five IC's that are probably all counters. And then this one down there in the corner that might be having to do with the clock.

[00:05:16]So anyway, all the parts are identified by type of IC and by resistor value. And looks like most of the resistors are the same value.

[00:05:28]So it should be pretty easy to just figure out what goes where.

[00:05:34]You can't really tell it in the camera, but uh I'm testing the original LEDs that came with the kit.

[00:05:41]They don't have a very good diffused look to them. Although again on the camera, it doesn't really show what they look like to the naked eye. Here's a higher quality LED running with the same voltage and current and it just has a nicer diffuse look.

[00:06:02]So, these are from my own stock. They're what I use on all my projects. I'm going to use these instead of the ones that came with the kit. But the ones with the kit are at least good enough that if people aren't as picky as I am, they'd probably be perfectly happy with the original ones.

[00:06:19]The uh LEDs are marked with plus and minus, but not with the usual flatted circle, which is typically what's used for uh component layout silk screens.

[00:06:33]Um this presupposes that the kit builder has some knowledge of electronics and knows what to make with the plus and minus.

[00:06:42]Um the pluses are the anodess and the negative or the minus is the cathode. So the LEDs are pointing in that direction from the plus to the minus. That means the flat side of the LED would be facing the uh top here and the short lead which is also the cathode goes in those holes.

[00:07:14]All right, I put all the IC sockets on first.

[00:07:19]These are really cheap sockets. Most of them the pins were not really firmly mounted in the plastic carriers. And if you're not careful when you're putting the sockets into the board, you can push some of the pins right up out of the carriers. So, I was able to fix all of them except for one that is only up slightly and I left it alone.

[00:07:46]Okay. I have the resistors on the bottom half of the board and also the four dodes.

[00:07:57]I put all the capacitors along the bottom there. Um, and I put the first uh most significant digits, seven resistors for the LED, but uh it's getting too late. I'm not going to do the rest of those tonight.

[00:08:17]All right, I have all the other 1k resistors, which are the LED segment, current limiting resistors.

[00:08:25]They're all installed, and there's just a small number of pieces, including the discrete LEDs and the seven segment LEDs that need to be soldered on yet.

[00:08:37]Each of these LEDs comes with a protective film over the face that's supposed to be removed, but it's stuck on reasonably good. And um I grabbed the corner with a pliers to peel it off.

[00:08:54]the um LEDs.

[00:08:57]Each digit has a decimal point at one corner and that's supposed to line up with the image of a decimal point. That's for orientation.

[00:09:12]All right, the seven segment LEDs are soldered on. And uh I held off putting the discrete LEDs on until I got these on so I could make sure that the tops of the discretet are level with the tops of the seven segments.

[00:09:32]And a lot easier to do that when these are already in place.

[00:09:36]All right, the LEDs are soldered on.

[00:09:41]I did the usual trick of putting masking tape tight across the top of these and then dropping the LEDs were already in place and then doing it like that so the LEDs would fall down and touch the masking tape and then look at them this way and adjust them so the leads look level from this angle. Solder one lead of each LED. peel the tape off and adjust them for tilt left and right in this view and then solder the other lead and cut them off.

[00:10:16]By the way, my kit came with five LEDs and I'd pulled five new ones out of my parts bin as previously discussed, but I can only find four places to put the LEDs on the board. So, I think the fifth one was a spare or an accident of parts placement, but probably a spare.

[00:10:36]And the uh power connector and the two push button switches, which are marked in what I guess is Chinese.

[00:10:46]Everything else on here is in Western characters, but these are not marked in English.

[00:10:56]It should be fairly easy to figure out how they work, though.

[00:11:02]All right, all the IC's are plugged in now. And of course, you have to make sure with this row of five here, they're actually in alternating orientations.

[00:11:13]This one, pin one, is this way. This one, pin one, is over here. Pin one, pin one, pin one. So, notch, notch, notch, notch, notch. All the other ones are put in regularly. All notches to the left here. Notch to the left here.

[00:11:33]According to the schematic, the two push button switches are here and here. They're in essentially identical circuits.

[00:11:42]This one seems to influence the most significant two digits. This one influences the middle two digits. And there is no button for these. But there is the switch down here, which at first I thought was a power switch, but here that seems to be a hold switch. The clock is generated down here. Then the clock goes into the counters through that switch. So I think that's hold. You could set the clock a little bit in advance and then wait till the real time catches up with it and then engage the clock with that switch and then it would be synchronized at least at that moment in time.

[00:12:28]So let's see what's happening here. Um the overflow from the seconds goes down here and um is diode coupled into the enable of the least significant minutes counter and also going into there is this push button up to VCC conditioned. with a capacitor to minimize switch bounce. So I think you have to push that every time you want to index up through the count. I don't think this is going to work where you could hold it and have it ripple up. I think it's more rudimentary than that.

[00:13:14]And then the same thing here when the tens of minutes overflows it can then roll into the units of hours or you can push the button and increment it. So, I suspect we're going to find that this button here increments the hours, and this one's the one that's going to increment the minutes.

[00:13:34]And this is the one that will hold the clock in its current count, although I don't know which side is up at this point.

[00:13:47]Okay, initial test. I've got my bench power supply set to 5 volts, which is the nominal voltage for this. And if everything's working and I turn it on, I should at least get some displays.

[00:13:59]Let's see.

[00:14:01]Yay. And it is counting.

[00:14:05]And the discrete LEDs are flashing.

[00:14:10]If I move this switch down um up, yes, it holds it. It doesn't continue counting.

[00:14:20]And then I can move the switch down.

[00:14:23]and it'll resume counting.

[00:14:27]If I put it in hold mode and push this button, yes, I can increment through the minutes.

[00:14:41]And if I push this button, I can increment through the hours.

[00:15:00]and then take it out of hold again.

[00:15:05]And that's how you would set it.

[00:15:08]So far, it looks good. Everything seems to be working. I'll put it to a real test when I have more time, but I've got to go play a gig. Um, I'm going to build some sort of protective front for this.

[00:15:22]And on that, I'm going to put some red filter material, which will make the LED displays a lot easier to read in normal room lighting.

[00:15:32]And then I'll probably mount it on a piece of wood or maybe a piece of aluminum.

[00:15:38]And um I've got to go through my box of derelict USB power supplies and find a sacrificial one that I can use to power this long term. Now the clock is running here and when I look at my power supply, it's pulling about 65 milliamps.

[00:15:59]So any USB power supply is going to be way more powerful than this clock actually needs. It's not exceeding. So, well, it does go a little bit into depending on I think the combination of digits that are on the moment. It draws a bit more or less current, but I think probably even 100 milliamps would be more than enough. And most USB power supplies are good for at least an amp.

[00:16:28]So, I have a little bit of finalizing work on this yet, but it looks like it's uh basically working.

[00:16:35]All right, I found a likely candid in my storage tub full of homeless power supplies.

[00:16:44]This is actually one from an old cell phone back when I was using Motorola products.

[00:16:51]AC power supply. Universal input. So, it's a switching power supply.

[00:16:57]5 volts regulated 550 milliamps. So, um, this is old enough where they weren't universally at least 1 amp, but it's still way bigger than necessary for this clock.

[00:17:14]And it's got a USB mini um, plug on it, which I will cut off.

[00:17:24]And you can tell this is uh only for powering because the uh cable only has the two leads. There's no data leads in this. It um some of the more modern power supplies that I've cut the leads off. They may have some sort of intelligence in there that can can communicate with the phone or whatever.

[00:17:47]I'm not sure. But I've seen ones with all four wires in them, even though it's just quote unquote a power supply. So, this is extra simple. I just need to figure out which one's positive. It's probably the one with the white stripe.

[00:18:02]All right. I tested this with my um DC voltmeter and uh it is indeed 5 volts, really close to it. And although I didn't throw it on a scope, I just put the the meter in AC mode and checked to see if there was any AC component and it said about 6 molts, which isn't surprising. It doesn't need to be all that clean.

[00:18:32]And the stripe is the positive side.

[00:18:37]And it looks like the clock is perfectly happy with that power supply.

[00:18:43]All right, I'm checking the frequency of the clock with my frequency counter. 70 32767 MGHertz and it's supposed to be a 32.768 megahertz. So, that's pretty darn good.

[00:19:05]I'm not going to quibble about that.

[00:19:08]It's much more accurate than I thought it might be.

[00:19:12]Almost dead nuts on.

[00:19:16]And so, by the way, I'd earlier guessed that this was the IC used for the clock, but it's actually this one.

[00:19:23]It's one right next to the crystal. Of course, this one's next to the crystal, too. So, I had a good guess.

[00:19:31]Okay. I have a couple pieces of [snorts] red filter material.

[00:19:37]And uh I'll do a test fit.

[00:19:42]That's what it looks like without the filter. This is what it looks like with the filter. Market improvement.

[00:19:50]I just need to cut these to size and stick them on with a tiny bit of superlue.

[00:20:01]All right, there's the beauty shot.

[00:20:29]Uh this is setting the clock. By the way, you can see that this is a 24-hour clock.

[00:20:42]And I have it in hold. The switch here is in this direction. That keeps it from counting.

[00:20:48]I've got it held here at 10, 13, and 27 seconds. I cannot set the seconds. I'm just waiting for my atomically synchronized or GPS synchronized clock to come around to 10, 13, and 27. And I'll slide the switch here down and allow it to start counting.

[00:21:11]Okay, I've got it synchronized to my most accurate clock uh within 1 second anyway, human reaction time. So, I'm going to come back a little later today and see if it's still that close.

[00:21:35]Well, it's actually the next day. I forgot I even had this running.

[00:21:38][laughter] Uh so flash to my nearest atomic clock here or GPS base clock. So 48 37 38 39 40 41 42 43 Yeah, 1618. It's the same time. It's this is about 1 second off and it was when I set it. So at least over the course of a day, it seems to have maintained its time. So reasonably accurate.

[00:22:20]I uh did clean the back of the board of all the solder flux. I'd probably said earlier that this one capacitor here, this single electrolytic capacitor, probably isn't necessary, and it isn't.

[00:22:34]But I found out that actually it does hold enough uh energy to keep the CMOS IC's temporarily powered uh at least enough that they don't lose their status.

[00:22:52]So, for example, I had it keeping time here and then I uh disconnected the power for, you know, maybe 15 seconds and reconnected it and the time was still correct except it was 15 minute or 15 seconds slow. So, the clock stopped, but the IC's that were holding the count retained their count during that time.

[00:23:20]But if you disconnected it for a longer period, then it'll just go back to zero like um it has done here recently.

[00:23:30]I decided to experiment a little bit. I ordered from Amazon a inexpensive cheap trim potentiometers in the poparad range. It's an assortment so there's different values.

[00:23:43]Uh they're really intended for Arduino projects. They seem to be pretty decent quality.

[00:23:51]Um, so I'm going to try juryrigging one of those up to here and see if I can use it to dial in the frequency even more precisely and thereby get the most accurate possible version of this clock.

[00:24:09]Those should arrive tomorrow morning, so I shouldn't have to wait too long. and I can just tack it on the back of the circuit board um and try to add capacitance across one of these. The data sheet stipulates one specific capacitor of these two that should be the adjustable one.

[00:24:31]Uh on the other hand, one of the resistors that's in this circuit is not according to the um its value is not according to the data sheet recommendations.

[00:24:42]Uh, so I'm still going to try adjusting the capacitance and see if I can dial it in even closer to the um ideal frequency.

[00:24:56]Well, I had sent back the trim capacitors I ordered from Amazon. That was the assortment. They were just incredibly cheap, lowquality.

[00:25:06]Um, I couldn't get any stable capacitance out of any of them that [snorts] I tried, at least out of the several I pulled out for testing.

[00:25:16]And uh, I said, "Well, I'm fussing around here with some low-end Chinese stuff, maybe even ones that are being sold cheap because they're factory rejects or something.

[00:25:28]So, uh, I decided to look for the kinds of things that were probably being copied to make those cheapo ones and go with a good brand.

[00:25:42]Um, in this case, it was Edmire Electronics/West Company doing business as EW Electronics.

[00:25:54]Um, there's a Digi Key part number. It's a 7 to 40 poparad trim capacitor.

[00:26:02]So I thought that ought to span the uh 33 poparad caps that are currently in the oscillator circuit.

[00:26:12]But I'm just going to put it on one of my capacitance testers and make sure that I understand how the rotation works and probably set one of these to about 33 as a starting value.

[00:26:26]and tweak from there.

[00:26:29]Actually, these things aren't winning any awards either.

[00:26:36]You can see that piece of plastic flash that's covering up part of the adjustment hole.

[00:26:43]Just sloppy um manufacturing.

[00:26:48]This one looks a little cleaner.

[00:26:51]This one actually looks about like you'd expect it to be. And there were none of them in the ones from Amazon that looked like you would expect them to be that way.

[00:27:03]Okay, that actually worked. Um, I was able to dial in 32768 hertz or 32.768 kHz.

[00:27:15]I'm monitoring at the output of the oscillator pin down there.

[00:27:21]This is a little tricky to do onehanded, but uh let's see here.

[00:27:31]32 768.

[00:27:36]That's closer than it was before. I don't think I'm going to get it any better than that.

[00:27:41]So, um it's not so obvious there, but I couldn't get the pin out to of the uh trim pot to fit the holes in the circuit board. And by the way, that is the capacitor you need to remove. It's the one on the right side of the crystal.

[00:28:00]Uh it'll work better on that side than replacing the other one.

[00:28:05]I had it initially dialed into approximately 33 poparads and then just tweaked it very slightly from there. So it was really close to start with. I had to solder on sweat solder on a couple of cut off resistor uh leads and then stick those through the holes in the circuit board.

[00:28:27]Um because I couldn't get enough clearance.

[00:28:31]I was just going to sweat the tips of the trim cap onto the holes of the circuit board, but I couldn't get the soldering iron in there with all the IC's around it, so I did it the other way. But that actually worked really well. I'm pleased with that.

[00:28:51]All right, I've reset the clock to the current time using my GPS synchronized clock.

[00:28:57]Uh, but of course, there's a little bounce on this switch.

[00:29:01]So, when I took it out of freeze mode, it jumped a few seconds.

[00:29:06]Um, so it's actually about uh it's about 3 seconds ahead of the uh GPS clock.

[00:29:19]So, let's see. 22, 23, 24, 25.

[00:29:24]So, so like well 3 seconds ahead.

[00:29:29]Um, so I'm going to let it run for a little while and just verify that it's accurate and then I'll put it to bed.

[00:29:42]All right, it does seem to be keeping good time and uh so I don't need to film any more of this.

[00:29:53]All right, this is the schematic.

[00:29:56]Um, it was not included with the kit.

[00:30:02]You think they could have thrown in a sheet of paper with the kit, but uh, no. Um, but in the Amazon listing, one of the photos of the product of the several that were there is actually like a photo of the schematic. So, it's not great.

[00:30:23]Um, it's kind of a little fuzzy, a little bit out of focus, but for the most part, the uh numbers and letters can be read adequately, at least the bigger ones. Some of the small ones, it gets like I think this says DSP for display, but it's hard to make out the letters. Uh, but certainly with pin outs and things, it's adequate. The parts of the numbers kind of fade out a little bit. And these uh lowercase letters for the identification of the LED segments are also hard to read in some cases, but it's a usable schematic.

[00:31:03]So I'm going to do a little theory of operation here.

[00:31:08]Um so first off, nominally this circuit should be powered from 5 volts, but it can be more or less. All the logic on here is cos and cos can work from, you know, 3 volts or something up to at least 15 volts. I did designs back in the early 80s that were all 4000 series CMOS just like these that ran off of 18 volts, which at the time was the highest recommended conservative voltage rating for those IC's. And I know those products are still in operation after all these years, so I know it doesn't kill them.

[00:31:55]But um a lot of the older data sheets, many of which are dating back to the '7s, um have a 15V maximum rating. Anyway, it's immaterial here. You're not going to run it that much. Um because USB power is 5 volts, that's a good common power supply. There is this electrolytic capacitor here. I mentioned it elsewhere in the video.

[00:32:23]uh it's a 100 microfarad capacitor and I think its purpose is not to filter the power supply but rather to um help bridge over temporary power interruptions. For example, you want to move the clock from one place to another. You can unplug the power supply from the AC outlet, you know, walk across the room, plug it back in, and while the timing will stop during that period, there's still adequate power here, you know, even as the voltage is dropping for the counter IC's at least to maintain the most recent time value. So you might, you know, if you walked across the room and plugged it in within 15 seconds, you'd be 15 seconds behind on the seconds reading of the clock.

[00:33:19]But, you know, not too terrible.

[00:33:22]So, I think that's what that's there for.

[00:33:27]And of course, if you powered it from some unregulated uh power supply that might have some ripple on it and so on, this can help with that.

[00:33:41]So, there is a total of uh five different types of CMOS IC's in here. I'll start with the easiest one. It's the 4081.

[00:33:55]Again, these are all 4000 series, so they all start with a four. This is a quad twoinput and gate package. So, four and gates, two inputs per.

[00:34:09]This is gate A, B, C and D. Only gate C is used in this clock circuit. The other three gates are unused.

[00:34:18]Another part that is used uh initially it's only used once I believe. Let's see. Is that correct?

[00:34:32]Yes.

[00:34:34]Um it's a 4013. I see.

[00:34:41]It's a dual DType flip-flop.

[00:34:46]The flip-flop one is on all these pins.

[00:34:50]Flip-flop two is on these pins. The D is one of the simplest types of flip-flop.

[00:34:57]And uh what you've got is a clock input, a reset input, the D input, and a set input. And then there's the usual Q output and inverted Q output. and then you duplicate it again for the other one. On this clock circuit, the uh second flip-flop is not used. The next type of IC that's utilized is a 4060 460.

[00:35:26]This is a 14 stage binary ripple counter. So, it actually has 14 flip-flops in it. Each one set up to divide by two.

[00:35:37]Um, so what you've got is it's also has a uh provisions for a crystal or RC oscillator built into it.

[00:35:48]So you'd hook up some resonance circuit whether it's a a RC resistor capacitor combination or a crystal and that involves an input and an output.

[00:36:08]the signal that's sent out to the resonant circuit and then the signal that's fed back in and it goes around and around at the uh frequency of the resonant circuit and then you can actually use either of these two outputs. One's inverted from the other.

[00:36:28]You can also just force feed a clock from some other circuit into this without using any resonant circuit here because this does need a clock to operate. So whether you use the internal oscillator or if you just force feed it an external clock, those three pins are for that purpose. And then it just starts dividing everything down.

[00:36:50]It doesn't bother to give you the first few divisions because normally you're going to run a a crystal oscillator. It's going to be running in the kilohertz or megahertz or whatever.

[00:37:00]There's not much point in seeing the first few divisions.

[00:37:05]The first, second, and third divider outputs are not brought out to pins. But output four here is the first one.

[00:37:14][clears throat] And then uh it jumps around. Output five, output 6, output 7, 8, 9, and 10.

[00:37:23]11 is not brought out. I don't really know why. And then outputs 12, 13, and 14, that's the last flip-flop output, are all brought out. So each one is half the frequency of the first one. Uh the crystal oscillator on here, this is the 4060, is running at 32.768 kHz or 32,768 hertz.

[00:37:51]And that's a binary value. So if you divide it down um I actually wrote the values down here.

[00:38:03]If you take the first available output which is the output of the fourth divider it's going to be uh and running at 32.768 kHz. Once it gets divided by 4 that's 248 hertz. The next one is 1024 hertz 512 256 128 6432 and as I said the next one isn't brought out so we skip 16 and then uh output 12 gives us 8 hertz 13 gives us 4 hertz 14 gives us two hertz so with the divisions possible within this IC and using a standard uh frequency crystal 32.768 is a standard value, readily available, inexpensive.

[00:38:58]You'll end up with two hertz here. Well, what you really want is one hertz. So, there's one more flip-flop, and that's in the um dual D flip-flop I mentioned before. This one right down here.

[00:39:13]You feed that into the uh input of this one. and with its inverted Q output tied back to its D input and then clocking the clock input. The Q output is a divided in half version of the clock input. So it goes from two hertz to one hertz. So you get one pulse per second.

[00:39:38]Now that signal is used directly even though it doesn't clearly show it here.

[00:39:43]The schematic is drawn in the way that if you just name something like putting one hertz next to a line that anywhere else in the schematic that has a line that says one hertz is presumed to be connected electrically.

[00:39:58]Uh so the decimal points are here.

[00:40:02]Uh you've got two LEDs here for one colon and two more LEDs for the other colon.

[00:40:10]And uh because you're assuming 5 volts here, uh the LEDs will turn on when the one herz signal is logically low.

[00:40:24]And that's one hertz down here and one hertz here. Uh so when that's low, current will flow through. And just pulling 1.2 volts out of the air as a common uh voltage drop for a red LED.

[00:40:40]uh and then subtracting the remainder by the 470 ohm resistor that's here for current limiting, you'd end up with about 6 milliamps going through here, which is a good value for an oldfashioned LED. Most modern LEDs right out of the gate can run perfectly nicely on around 1 milliamp.

[00:41:05]Um, certainly the LEDs I put in mine to replace the ones that came with the kit, I've used those for decades in my own designs, running at 1 milliamp, and they're perfectly bright. So, here they're getting hit with about six times that current, but that's within their range. It's not going to burn them up.

[00:41:27]It's just that they're maybe a little needlessly bright. Still, they look okay to me running at that current.

[00:41:36]So, anyway, we've got the one herz signal and then we feed it through this switch here, switch three. This is the pause or freeze switch.

[00:41:47]And looking at the switch from the front, if the paddle is down, that's the normal position. and the switch is closed and it passes the one herz signal on up to IC9A.

[00:42:01]The A means it's half of IC9 where IC9B would be the other half of the same IC.

[00:42:09]Uh so the clock signal goes right into here. But if you open the switch, that's what happens when the paddle of the switch is up.

[00:42:20]then it's open and the clock signal cannot get through this clock or this IC here responds to a clock on its enable input that's EN there it responds on the negative transition. So when it goes from high to low that's when this increments its count it doesn't respond when you're going from low to high or just sitting at high or just sitting at low. it's always on the falling edge um that it clocks. So, if you had this switch open for a while, like you're freezing the the uh the time for a while, then this resistor here pulls this input low, the enable input low.

[00:43:10]And since it's just sitting at low, it doesn't get clocked.

[00:43:14]When you reconnect this, the next time the one herz signal goes to logic high, immediately charges up this small capacitor and the signal goes high here. And then when it next time falls, then it'll treat that falling signal as a clock signal. And this capacitor is going to get dragged along by the the output of this IC. So, it's not all that significant. But when you open this um what it does is it discharges this capacitor through this resistor.

[00:43:55]So it uh allows this to fall gradually over you know a small fraction of a second and that helps with uh debouncing this switch. If the switch chattered a little bit when you're sliding it, you might actually get some extra pulses through. So, this RC here acts to debounce the switch. It has the side effect where uh it'll cause one additional count of the seconds.

[00:44:30]Uh if the low high low to high transition of the clock happens when the switch is opening.

[00:44:41]Uh so I said that awkwardly but I think you get the idea. It can cause one false increment but that's only 1 second.

[00:44:54]The next IC we have is the 4518 and I sketched it out here. This is a dual synchronous divide by 10 counter with BCD outputs. So it's two divide by 10 counters in one package.

[00:45:12]This is one side of it. This is the other side of it. You have a clock input. You have an enable input.

[00:45:20]You have the BCD outputs weighted 1 2 4 and 8. Sometimes these are called A, B, C, and D. It just depends on the uh the data sheet, which manufacturer put that data sheet together. I personally prefer calling them 1248, but I understand why some people call them ABCD because it doesn't make it sound like the pin number. And then there's a reset.

[00:45:47]Um, depending what you're doing with these. If you're holding one of these inputs low, then the other one acts as the clock. If you hold that one low, then this one acts as the clock. But it depends. Uh, if you're using the clock input, it responds to a low to high transition. If you're using the enable input as the clock, it responds to a high to low transition. In this case, the clock is supposed to be responding to a high to low, which is why the clock signal goes into the enable instead of into the clock input. And the clock input is tied to ground, as is the reset input because we're not using it. And then the BCD output appears on these four pins here. It's called Q12 uh 1 2 3 which is not all that useful.

[00:46:43]Um I put in the binary waitings here 1 2 4 and 8. Although because it's a BCD counter it only counts up to a binary equivalent of 9 before resetting back to zero again.

[00:47:00]So this is IC9A. That's half of one of these. And then right next door is IC9B.

[00:47:08]That's the other half of one of these.

[00:47:11]So these two counters are in one IC. And then this is 8 A and 8B. That's in the next IC.

[00:47:22]7 A and 7B is in the third IC of that type.

[00:47:31]And then as this is counting up, the BCD information is set up to the next IC, the 4511.

[00:47:41]And I have the 4511 sketched out here.

[00:47:44]This is a BCD input seven segment latch decoder driver IC.

[00:47:54]So it has three functions built into it.

[00:47:57]It has a latch to latch incoming BCD data.

[00:48:03]It has a strobe or a latch enable input which tells it how to to do its latch function or not. You can disable the latch function and not have it do any latching.

[00:48:17]It's also decoder. It decodes the BCD to the appropriate pattern of segments for a seven segment LED to get a number displayed that corresponds to the value of the BCD input. And then finally, it's a driver. It drives current through each of the LED segments.

[00:48:42]So it has all three of those combined.

[00:48:46]Uh in this particular application, in this clock circuit, there's two additional inputs. You can blank the display, make it show nothing, even if it's being commanded by the BCD to show some number. If you pulled this low, it's an active low input. That's what this line means. Uh if you pulled it low, then it would blank the display. If you pulled the LT or lamp test input low, it would turn all the segments on. So, no segments, all the segments. But we're not implementing either of those in this clock circuit. So, both of those inputs are being tied to the uh positive power supply, which is logic one, thereby disabling those functions.

[00:49:34]We're also not using the strobe. The strobe works positively instead of negatively like these. So, you'd have to bring the strobe input high in order for it to latch the data, but we're not doing that here. It's always updating real time. So, this is disabled by tying it to circuit ground or logic low. And then we have the uh four inputs for the BCD. The A or 1, the B or 2, the C or 4, and the D or 8.

[00:50:10]So the numbers are the binary waitings for the BCD signals. [snorts] And then the ABCD is the other convention.

[00:50:20]And then it's conventional to use lowercase letters when referring to segments of an LED display. So we have A B CDE E FG here. This IC does not know what to do with decimal points. If you have decimal points, they get driven by something other than this IC. So, jumping back to here, here's one of those IC's.

[00:50:45]It does in fact have its lamp test and um blanking inputs tied to VCC. And it does have its um latch enable or strobe input tied to ground as do all the other ones.

[00:51:07]So again, all that means is whenever this counter changes its BCD value, this chip will immediately process that, convert it to seven segment uh pattern and send it on its way to the uh LED.

[00:51:22]And then here you have your ABCDE EFG.

[00:51:25]Here it's not following the convention.

[00:51:27]It's showing them as uppercase.

[00:51:30]Each one goes through a current limiting resistor here. They're all 1k and then we're into the seven segment display. There's only one seven segment display associated with this decoder.

[00:51:47]This whole thing is not multiplexed.

[00:51:50]It's a big costsaving and parts count reducing and simplifying approach to multiplex displays.

[00:52:00]And you actually could have done that here. It would have been possible to multiplex this display. But part of the whole idea of this kit is to present everything in its most basic straightforward educational kind of arrangement. So everything is being done uh old school.

[00:52:19]Um and then because the current is going into each of the segments, it has to get out somehow. And there are two separate cathodes here. This is a common cathode display. That means that all of the segments. Each one's an LED.

[00:52:35]And um the anodes are the ones being driven here. And then the cathodes are common. There's essentially only one for the whole display. But here it comes out on two different pins. I don't think it's one cathode for half the segments.

[00:52:50]It might be, but I doubt it. It wouldn't make any sense. I think it's just that they happen to bring out uh the cathode to two different pins for you know convenience of circuit board layout or whatever and that does return to circuit ground. So pretty straightforward. The decimal point input is not connected to anything cuz it's not used in the clock.

[00:53:13]So again this uh clock chip here is counting up the least significant seconds. So it's the seconds, not the tens of seconds. So it's expected to go 0 1 2 3 4 5 6 7 8 9 and then immediately go back to zero again and count up again. There needs to be some way to carry the output to the next uh digit which is the uh tens of seconds. And there's a similar uh counter. And indeed it's the other half of the same chip that has this one.

[00:53:50]And we've got to look at this here and see are we using the clock input or the enable input. We're using the enable so we know it's going to respond to a falling signal.

[00:54:05]And I pencil that in there. That's what that circle means when you're doing logic di or timing diagrams.

[00:54:14]If you show a waveform dropping like that, for example, and put a circle around, that means that the only thing that cares about whether it's high or low or going high or going low, it only cares about the going low part, the uh the signal dropping or transitioning low. There's a lot of different terms for it, but we know from the fact that we're using the enable input that this chip is only going to react to this going from high to low, a high to low transition.

[00:54:51]So, we have to think about when does the eight weighted BCD output go from high to low?

[00:55:07]Well, if we look at the uh timing chart for that, because it's the eight weighted one, when the number being displayed would be an eight, that's when that pin comes on. And anything higher than that. So, here's a timing diagram.

[00:55:27]um all the way from zero and then 1 through 7 and up to eight it's low. But at the moment the clock goes to or the counter goes to eight, it goes up to high. It jumps at that exact moment. And then for the rest of it being 8 and for the time when it's nine, it remains low, but then the counter resets back to zero. And we know that at zero. And I should have penciled that in to make it clearer.

[00:56:03]There.

[00:56:06]So it's low all the way from 1 through 7. On eight, it goes high. It stays high through the duration of eight and through the duration of nine. And then it drops back to low when it resets back to zero.

[00:56:26]So since we know the next stage is looking for a falling value, a high to low transition, when that happens is when this counter resets back to zero. So we know it'll count from 0 up to 9. When it sets back to zero, that's exactly when you want the next digit to increment. So that's how that works. it'll detect that falling signal and increment its count to the next thing. Well, now this digit is tens of seconds. So, we know it can only go up to 60.

[00:57:05]And actually on 60, it has to reset to zero. So, it'll count from 0 0 up to 59 seconds. And when it actually tries to go to 60, it's going to immediately reset back to 0 0 without staying on 60 very long, but it will be on 60 very briefly.

[00:57:27]So, what we're trying to do is trap that condition here.

[00:57:32]And uh we're going to use the two- weighted and the four-weed outputs and they're going to be combined in an and function.

[00:57:42]The two- weighted one is low and on two it goes high. It stays high for the duration of two and the duration of three. When it gets to four, it goes back to zero. Stays there for the duration of four, the duration of five. And then at six, it goes high. But we don't really want a six to be displayed.

[00:58:09]But we have to wait until it would be a six. So as soon as it tries to go high, then this input is high. At the same time, uh we're also double-checking to make sure that we're um not going to trigger on this part of it.

[00:58:33]You don't want to trigger on a two or a a three. So, we combine the four-weighted signal, which is on from four until six, with the two- weighted signal, which is on from 2 to 4 and from 6 to whatever.

[00:58:54]Of course, we're resetting on six. But when those two conditions are true, then we know that this thing is trying to display a six.

[00:59:02]It takes that signal, it produces a very short pulse. And the reason it's so short is, sorry, my hand is getting my arm was getting tired and I was jiggling the camera around too much. So the very moment that you would get a six here, it turns this high, it reaches around and it goes to the reset input of this counter and sets it back to a zero again. So it goes 0 1 2 3 4 5 6 and the moment it goes to six this gate turns on and resets it. So it goes back to zero.

[00:59:43]So while it is temporarily displaying a six it is for such a short amount of time you know it's like speed of light.

[00:59:50]It's as fast as this logic can process it and issue the reset. Uh, so you'll never see a six displayed, but technically it was on a six for a very brief moment. So you'll actually get a pulse here, a very brief pulse as I wrote. I actually had a uh a logic analyzer and also I tried a logic probe on this. My logic analyzer is kind of old and it's not very fast. Neither the logic analyzer nor the logic probe could respond to the brevity of this signal.

[01:00:24]It acted like it never did it. But of course, it has to be doing it or this would never reset.

[01:00:32]So that's how we can count up to 60 seconds or 59 displayed.

[01:00:42]And then that brief pulse will go through this diode, drop the voltage across this resistor.

[01:00:51]And the rest of the time when this is not logically high this diode is not conducting because it's reverse biased under those conditions and therefore this signal would just be left you know flapping in the breeze. So this resistor pulls it down to make sure it sits at logic zero. But then when we get the brief pulse through here and the 4148 diode is quite a fast diode. So, it's plenty fast to turn on within the duration of that very brief pulse and propagate the pulse through and it goes into the enable input of the next counter which is the units for the minutes.

[01:01:36]Now, in order to set the clock, you can set just the minutes by incrementing the minutes over and over and over. But the only thing you're really doing here is incrementing the units of the minutes.

[01:01:57]And then of course it'll roll over to the tens of minutes. So if you're trying to set it up near 60 or whatever, uh you're going to push this button quite a few times.

[01:02:11]But it's not really that hard to push it 60 times. You can do that in a few seconds if you try.

[01:02:17]So regardless of what this is doing here, and most of the time it'll sit there doing nothing cuz this is only going to pulse once every minute.

[01:02:28]Uh you have this switch here going to VCC or V+ and it has a capacitor to ground and then it goes through the diode. So again, normally this is being pulled low by this resistor to ground. When you push this switch, it pulls this high. It forward biases the diode. It conducts through. It drops the voltage across the resistor. And that positive going pulse, not a brief one like this, but as long as your finger's on the button, we'll come over here and turn this on, which does absolutely nothing because this enable input is looking for a high to low transition, not a low to high transition. But then when you take your finger off the button briefly, this capacitor's charge will keep it high, but it'll bleed off pretty quickly. And it'll go away, and this will see the negative transition.

[01:03:28]So, it's actually incrementing when you take your finger off the button, not when you push it. But unless you just sit there like an idiot and hold the button down for a while wondering why nothing's happening, you're supposed to push it and release it.

[01:03:42]Um, this capacitor is essentially there to debounce it. So, if the switch chatters a little bit, you won't see this picking up a bunch of counts. The capacitor will slow it down. So, it just gets the overall intention of the button push, a single pulse going through. And that's how you can set the minutes.

[01:04:08]And then just like before, we have this counter for its for the units of the minutes. And it overflows just like the units of the seconds did.

[01:04:23]And it goes into the enable input of the counter for the tens of minutes.

[01:04:30]And everything else is identical. All the displays are driven the same way.

[01:04:34]The latch decoder drivers are all exactly the same.

[01:04:42]Well, we know now that this guy here is trying to count up to also 60 minutes, [snorts] not 60 seconds, but 60 minutes.

[01:04:52]But it's the same circuit.

[01:04:54]And the reason for that is, of course, because we're trying to count over the same range of numerical values.

[01:05:02]And once again we have the diode, the resistor, another push button switch, a capacitor, another diode, and this is for incrementing the hours. So it's exactly the same. And once again, it goes to the enable input of yet another counter. And this is for the units of the hours.

[01:05:24]And every time that rolls over, just like the units of the seconds or the units of the minutes, the units of the hours goes over and increments the next one, which is the tens of hours.

[01:05:40]So that gets you your normal counting, but with the hours, it's going to reset at a different time. It's going to do something different from what we've seen so far.

[01:05:51]Um, this is a 24-hour clock. It does not just count up to 12. It counts up to 24.

[01:05:58]Of course, it only displays 23 cuz it would reset on 24.

[01:06:04]Um, but you have to be careful that you only do the reset when you have the proper um display. So you can sit with a two on the 10ens, but you have to wait for it to get up to a four on the units. So it would be 24.

[01:06:28]So you're capturing the four-w weighted bit of the units which comes on at 4 seconds or four hours and turns off at 8 hours. and you're combining that with the two output, the two weighted output, which would be on whenever it's trying to display a two.

[01:06:58]And normally that would be on at two, off at four, on at six, off at 8. But we're not going to get that high.

[01:07:06]When this is sitting at a two and this one is sitting at a four, that means the display is showing 24. And the very moment that happens, this gate turns on and it resets both the units and the 10ens at the same time. So that's how it goes up to 24 and immediately resets back to 000 hours.

[01:07:31]Um, in a blink of an eye, you won't even see it. Once again, a very brief pulse occurring when it gets the 24 hours.

[01:07:43]So that is the entirety of this except I think I didn't really talk about the crystal oscillator very much.

[01:07:54]I said the 4060 IC um is set up to have a crystal oscillator or an RC oscillator or be fed an external oscillator signal.

[01:08:08]Um so here's the clock [clears throat] out and the clock out inverted those are outputs and then the clock input.

[01:08:20]This is the nomenclature of the whoever in China designed this circuit. I guess normally that's called oscillator in oscillator out oscillator out inverted or not.

[01:08:37]And there's also a reset input which is not being used. So it's tied to ground or logic zero.

[01:08:43]This is exactly the configuration that's recommended in the data sheet for the 4060 in so far as you use the uh inverted output and the input. You put a onemeg resistor across them and then they recommend a 33k resistor here but it's the same configuration otherwise. and then the crystal there like this. And then they recommend 15 poparads from here to ground and from here to ground. In this kit, they're using 30 poparads.

[01:09:23]Those are just optimizing the loading on the crystal so you get the most reliable operation.

[01:09:31]Again, they recommend in the data sheet that this capacitor be made adjustable so you can dial in the exact frequency.

[01:09:40]Crystals aren't absolutely dead nuts.

[01:09:43]You can't change them by very much, but by messing with the capacitance, usually just one of them, you can force them to operate slightly off their nominal frequency. And by that you can tune them to exactly the right frequency.

[01:10:02]So that's what that's all about. When I get my variable capacitor in the mail, I'm going to either parallel it across this. If that does the trick, maybe I need to lower the uh capacitance to get the right frequency.

[01:10:21]And if that's the case, then I'm going to replace it with a 30 poparad trim cap and then dial it down to a slightly lower value until I get the correct frequency. And we'll see how that works.

[01:10:36]But if I need it to be a larger value, I may just use keep the 30 poparad in here and parallel it with the trim capacitor and thereby add the two values together.

[01:10:50]All right, one more thing. I mentioned earlier that the only schematic I have for this clock is the one that came as one of the images on Amazon's uh sale listing and it does seem to be the same circuit.

[01:11:09]Uh however uh there are a number of component designations that are different. Um I have no doubt that this same circuit board design has been replicated by more than one company you know sort of producing it in parallel maybe and maybe they changed their uh silk screen on one manufacturer's version of the board. Um as far as I can tell by ringing out the components the circuit is the same but I'll go through the difference as I observe them.

[01:11:46]Uh, in case anybody else wants to mark up their schematic, uh, take a look at the silk screen for the four discrete LEDs that are used as the decimal points. If you see them labeled LED 1, LED 2, etc., then you're probably okay cuz that's what the schematic says. On mine, it did not say LED 1 2 3 and 4. LED 1 was D7. LED 2 is D8. LED 3 is actually D5. And LED um 4 is actually D6.

[01:12:25]The resistor that goes with D7 and D8 is actually R49.

[01:12:30]The resistor for D5 and D6 is actually R48.

[01:12:37]The capacitor across the power terminals is actually C6.

[01:12:46]The um hours increment push button switch, that's the left hand one that's closer to the power connector, is actually S3 instead of S4. The adjacent capacitor is actually C4 and D1 is correct. The nearby D2 is correct, but the 2.2K resistor is actually R46 instead of R45.

[01:13:14]Going over to the uh minutes increment, we have a similar thing. In this instance, the push button switch is correctly labeled as S2.

[01:13:24]The adjacent capacitor C3 is actually C5.

[01:13:30]D3 was okay. D4 is okay. The 2.2K 2k resistor near that is actually R47 instead of R46.

[01:13:40]When we get over to the U right lower right hand corner of the board near the slide switch for putting it in a freeze or weight state or hold state. Um it's it may be marked S3. It certainly is on the schematic. On my circuit board it's called S1.

[01:13:59]The nearby resistor is R45. That's a 2.2K. 2K and the nearby capacitor is C3 instead of C4.

[01:14:09]When we get over by the crystal, the crystal is Y1 instead of just Y.

[01:14:16]Uh the two capacitors are labeled uh the one closest to the IC between the crystal and the IC is C1.

[01:14:27]The other capacitor is C2.

[01:14:31]The uh 10meg resistor is R44.

[01:14:36]The 100k resistor is R43 and um I have to double check the markings for the LEDs. I also verified all these resistors that are the uh segment current limiting resistors.

[01:15:00]uh the markings on the circuit board and the markings on this particular version of the schematic seem to agree. Now, they only say, for example, R1 through R seven here.

[01:15:12]And then there's this 1K star 7. That's a multiplication sign. So, it's supposed to mean there's seven 1K resistors. And R1 through R seven. It doesn't say so, but it's from top to bottom. R1 through R7.

[01:15:27]And that's consistent all the way through here. 8 through 14, 15- 21, 22- 28, 29 through 35, and 36 through 42. I was looking around for something to put this in to just to keep the dust off of it.

[01:15:44]And um a while back, I had um a need for some boxes for my bicycle group to put things in for presentations. And I bought this. It's a 6x4x2 plastic box that Uline sells, but they only sell it in cartons.

[01:16:09]Um about the size of one of those little hotel refrigerators.

[01:16:16]So, you get 30 or 40 of them if you want just one. Luckily, they're cheap. But, um I dug around and found those and I think the size is about right. It's way too tall, but the other dimensions are probably pretty close.

[01:16:46]Yeah, it's not too bad.

[01:16:52]So again, it's um not even using the whole height.

[01:17:02]So I can snap the top off and probably cut these little little pieces off of there like that.

[01:17:13]And likewise these hinges.

[01:17:17]All right.

[01:17:18]Now I have the little 44 spacers I put on here just to get the bottom of it off whatever surface it's sitting on.

[01:17:34]And I can put this over this and it'll be a nice size. So I can either have a piece of wood behind that or a piece of metal to have as the uh base for that.

[01:17:49]Um, I got to go down in my shop and see what I can come up with for this.

[01:17:54]All right, I'm really kind of rushing through this, but I p found a piece of nice 1/4 in uh oak veneer plywood scrap and I cut it a little bit larger than the periphery of the plastic cover.

[01:18:10]And uh put some recessed holes in the back so I can put some 440 screws through. And then these I didn't recess. I did those earlier and they go into these little brass hinges I happen to have laying in a drawer.

[01:18:27]And I've already drilled holes in the plastic for the hinges. And I've got four more uh sets of 440 screws there to attach those with. And some rubber feet.

[01:18:42]All stuff from my junk box.

[01:18:45]All right, here's what I threw together very hastily.

[01:18:49]Um, I've got the board screwed down, the circuit board screwed down to the quarterinch plywood. I've got the hinges on there. I had to revise the dimensions a little bit to allow the hinge, the hinged lid to go all the way up.

[01:19:06]Uh, and uh, I tuck the cord from the USB power supply back through the hinge area under a slot in the case.

[01:19:16]And it closes down like that.

[01:19:26]Keep the dust off of it.

[01:19:31]All right. There's where it sits in my shop next to my internet radio, which is a good source for calibrating it if I need to.

[01:19:43]You might as well go somewhere and no point in building it, getting it all hacked, and then throw it in a drawer somewhere. So, at least I can see this um pretty much across the room in my shop, which before I didn't have any timekeeper down here besides my watch, which isn't the most accurate.

[01:20:08]So, I'm happy with the outcome.